This invention relates to the production of hydrogen, and in particular to a new steam reformer catalyst and process for using same, in which the catalyst is based on nickel impregnated on a previously shaped support of alumina.
The steam reformer process is a conventional method for preparing bulk hydrogen or hydrogen-containing synthesis gases for the manufacture of ammonia or methanol or for the OXO process. Gaseous hydrocarbon is reacted in the presence of steam and optionally air in the presence of a nickel catalyst in a reformer furnace under pressures up to 50 bars at temperatures ranging between 500.degree. and 1,000.degree. C., the ratio steam/carbon in the reaction mixture generally ranging between 2 and 5. In an optional secondary reformer, the gas issuing from the primary reformer having a temperature of 750.degree. - 800.degree. C. and containing H.sub.2, CO, CO.sub.2, H.sub.2 O and CH.sub.4 is reequilibrated at temperatures up to 1,000.degree. C. in order to reduce the methane content, the temperature being obtained by introducing air.
When employing methane, the reactions in the reformers are: EQU CH.sub.4 + 2H.sub.2 O .fwdarw. 4H.sub.2 + CO.sub.2 EQU ch.sub.4 + h.sub.2 o .fwdarw. 3h.sub.2 + co
In addition to methane, other gaseous hydrocarbons can be used, e.g., natural gas, ethane, propane and butane.
Catalysts impregnated with nickel are manufactured by preparing a refractory support, soaking the prepared support in a nickel salt and calcinating the resultant catalyst in order to convert the nickel salt into nickel oxide. The advantages of such catalysts are known. For example, their activity, for the same nickel content is higher compared to catalysts where nickel is coprecipitated with the elements of the support. It is also unnecessary to reduce a calcined impregnated catalyst with hydrogen prior to use in order to convert the impregnated nickel oxide into nickel. Furthermore, the catalyst support can be prepared by ceramic methods which obtain a higher mechanical strength.
The catalysis rate is limited by the diffusion rate of the gaseous reagents in the catalyst elements. Therefore, attempts have been made to increase the contact area between the reagents and the catalyst. Whereas it is known that the contact surface increases with smaller catalyst elements, the pressure drop in the reformer furnace is deleteriously increased. To counteract the pressure drop, there have already been used ring-shaped elements having a large contact area but causing only a rather slight pressure drop. However, such ring-shaped elements are prepared by tabletting and their manufacture is costly.